Cleaning treatments are employed in a variety of metal forming and coating processes. Cleaning operations remove oil and debris and precede conversion coating or other coating operations. Satisfactory treatment of such metals requires that any dirt and lubricants on the metals (from the forming, drawing and ironing operations) be removed. Both alkaline and acid cleaners are employed in the metal cleaning area.
In cleaning aluminum, both alkaline and acid cleaners provide effective cleaning, but present serious problems. Acid etching and cleaning with, for example, strong acids like sulfuric acid with hydrofluoric acid produce clean mirror bright surfaces. However, the use of acids for cleaning present safety and effluent disposal problems and also requires stainless steel equipment. For these reasons, alkaline cleaning and etching processes are favored in the aluminum processing industry. However, alkaline cleaners also produce effluent disposal problems.
An alkaline cleaning and etching process for aluminum is disclosed in U.S. Pat. No. 4,477,290 to Carroll et al. The low temperature alkaline cleaning and etching solution for aluminum disclosed comprises alkaline metal hydroxides and a chelating agent at temperatures of from 80 to 130.degree. F. No other ingredients such as wetting agents which would cause foaming problems are required.
U.S. Pat. No. 4,521,332 to Milora discloses a highly alkaline aqueous cleaning dispersion for strip steel which comprises sodium hydroxide, a bulking agent such as sodium carbonate and a poly(acrylic acid) dispersing agent.